This invention relates to the transporting of bulk commodities by train, which train has on-board facilities for unloading the bulk commodities; and more particularly to such train having a conveyor running its entire length and supported between the train wheels for receiving the commodities from overlying hoppers, and discharging them at one end of the train.
Rail transportation is generally recognized as being more economical than truck transportation for bulk commodities such as aggregates. Large quantities of such commodities can be moved by a small crew at low cost. However, rail transportation frequently loses out in competitive situations because of the cost of unloading, stock piling, and delivering the commodity to the ultimate destination.
Even though large quantities of bulk material can be transported at low cost from one terminal to another, the burden is placed on the unloading facility to maintain the economics of this method of transportation for the purchaser of the commodity. If the unloading is slow, and the train is therefore delayed for a substantial period of time for the unloading to be accomplished, there is an added investment cost per ton handled for the use of the railroad equipment. One problem, in this regard, is that rail transportation is a 24-hour operation while many of the industries it serves operate only during daylight hours. Often a train makes good speed from origin to destination, only to be delayed several hours waiting to be unloaded. Each hour of delay adds to the transportation cost as much as an additional 25 to 50 miles of haul.
As an example of the efficiency of rail transport for bulk commodities, a train with a two-man crew pulling 1600 net tons at 55 miles per hour would be producing 32 times as many ton-miles per hour as a dump truck driver hauling 25 tons at 55 miles per hour.
Another problem effecting the efficiency of rail transportation for bulk commodities is that, under current methods, the quick unloading of a commodity train requires high capacity equipment and facilities which are idle most of the time. Such high capacity equipment and facilities are expensive, and add significantly to the investment cost per ton handled.
The following are some of the methods which are currently used for the unloading of bulk materials from trains.
Bottom dumping hopper cars are equipped with automatic doors that are opened automatically as the cars move over a pit, where the pit facility includes a feeder and a conveyor. Either a pit or an elevated trestle is required for this method, so that this method is ruled out at many locations. Obviously the providing of a pit or trestle facility with associated conveyor systems is expensive.
Another method involves the use of rotary car dumpers; and these are commonly used for unloading coal at electric generating plants. Again, the equipment for unloading the cars is highly specialized and expensive.
Side dumping cars have been used for many years, but cannot be dumped on level ground. They require elevated track on a built up embankment for example, so that the dumped material will flow over the side of the embankment and not flow back over the track.
Finally, backhoes or other unloading equipment are used to unload standard gondola cars. These methods are generally slow, promoting the delay problems mentioned above.
To take maximum advantage of the efficiencies of rail transportation, a special type of train is needed to deliver bulk commodities on any track, at any time of the day or night, with no labor required other than the train crew. Such a train would make optimum use of labor while providing incentive wages for the crew, and thereby reduce overall labor costs.
A self-unloading train which overcomes many of the above discussed disadvantages of rail transportation for bulk materials may be a "unit train" consisting of a plurality of hopper cars and a trailer car, the unit train to be pulled by a conventional locomotive.
Each of the hopper cars may include several hoppers having bottom discharge openings and associated gates for discharging onto an endless belt conveyor which runs the entire length of the train. The trailer car includes a transfer conveyor which receives the material from the train conveyor, and is movable on the trailer car to transfer the material to a selected point relative to the train.
With the unit train moving along a straight section of track, the material may be deposited in a windrow along side track by the transfer conveyor. Alternatively, the unit train may be unloaded while stationary, with the transfer conveyor discharging onto a portable stacking conveyor, for example, which will enable the deposit of the material in piles thirty feet high at least forty feet away from the track for example.
Applicants are co-inventors of a generally similar train having an on-board belt conveyor which runs the length of the train for receiving bulk materials from overlying hoppers. The earlier train design was developed to modify existing standard gondola cars, the structure of which included conventional center sills, couplings, bolsters, and two-axle trucks. Railcars of this design modified to include hoppers overlying the conveyor belt are able to carry the maximum allowable gross weight of a material such as crushed limestone, weighing about 85 pounds per cubic foot, with the center of gravity of the loaded railcar being maintained below the 96 inch limit.
It is desirable to use a train according to the applicant's earlier invention for carrying coal, for example, which weighs about 50 pounds per cubic foot. For a hopper car as above described to carry the allowable gross weight of coal, the hopper walls could be raised to carry more volume, but this type of modification would quickly raise the center of gravity above the 96 inch limit.
As an alternative to raising the height of the hopper walls, longer cars could be constructed. For example, rather than using a car having a length of 56 feet, the length of a standard gondola car, a car could be designed having a length of 90 feet for example. However, cars of this length create maneuvering and clearance problems, and require that the train have a longer straight track available for unloading. Trains of this type having a train length belt conveyor must be positioned on a straight section of track when the conveyor belt is being operated to discharge the load.
A much more desirable solution is to design a train including hopper cars wherein the load may be carried lower, enabling the height of the hopper cars to be increased without exceeding the 96 inch center of gravity height limit for the loaded cars in the United States of America.
An object of this invention is to provide improved equipment and methods for the rail transport and unloading of bulk materials.
Another object of this invention is to provide such improved equipment and methods whereby the unloading may be accomplished by the train crew at any time of the day or night, thereby eliminating idle time of the train equipment while waiting for the opening of an unloading facility or while waiting for the arrival of material receiving equipment or vehicles.
A further object of this invention is to provide such equipment and methods wherein the unloading does not require highly specialized and expensive unloading facilities or equipment.
Still another object of this invention is to provide such apparatus and methods wherein the unloading of the train may be accomplished efficiently in a very short time.
Another object of this invention is to provide such equipment and methods to minimize the expense of unloading bulk material from a transport train.
Another object of this invention is to provide such equipment and methods wherein the equipment includes selfunloading apparatus.
A still further object of this invention is to provide such equipment and methods wherein the equipment is a unit train having a train length conveyor.
Still another object of this invention is to provide such equipment and methods which take advantage of the efficiency of rail transportation by eliminating the need for a specialized unloading facility.
Another object of this invention is to provide such improved equipment and methods which enables the use of deeper hoppers to allow transport of the maximum allowable net load of lighter bulk commodities, while maintaining the required center-of-gravity height limit.
A further object of this invention is to provide such improved equipment and methods including a side sill car structure, enabling the bases of the hoppers to be located closer to the rails.
These objects are accomplished broadly in a train formed from a plurality of coupled hopper cars. Each hopper car is constructed to include a pair of side sills extending the length of the car for carrying the car load. The side sills are joined together by car structure providing an unobstructed longitudinal channel between the hopper car wheels and immediately overlying the wheel axles. A train conveyor, including a supply run and a return run, traverses the channel and extends the length of the train to discharge the material at the end of the train. The return run is supported immediately above the wheel axles. Troughing idlers are supported immediately above the return run for supporting the supply run. Each of the hopper cars includes at least one hopper having walls inclined at shallow angles from vertical to a bottom discharge opening, for gravity discharge of the bulk material to the train conveyor. Each of the hoppers includes for its discharge opening which are operable selectively to discharge the material from the hoppers onto the train conveyor.
These objects are also accomplished in a method which includes the following steps. Bulk material is loaded onto a train including a plurality of hopper cars, each having one or more hoppers. The hopper cars are constructed to include a pair of side sills extending the length thereof for carrying the car load, and providing an unobstructed longitudinal channel between the hopper car wheels and immediately overlying the wheel axles. The hoppers are formed with walls inclined at shallow angles from vertical to bottom discharge openings, for gravity discharge of the bulk material. The bulk material is discharged from the hoppers by means of discharge gates associated with the discharge openings. The material is conveyed from the hoppers to the end of the train, and discharged from the train, by means of a train conveyor traversing the length of the train within the channel.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawings.